The present invention relates to an endoscope, and more particularly, to a mounting structure of a cap which is detachably mounted on a distal end member of an insertable portion of an endoscope.
In an endoscope of the type having a structure in which a cap is mounted on the distal end of the insertable portion thereof, when the endoscope is inserted into a coelom with the cap mounted, it is necessary to completely prevent tee cap from falling off.
In the past, a cap has been mounted by fitting in a fitting groove formed on the outer periphery of a distal end member of an endoscope, or a cap having a female thread on its inner peripheral surface has been mounted by mating with a male thread formed on the outer peripheral surface of the distal end member.
With such a mounting structure, however, when the cap becomes loose while observing and operating with the insertable portion of the endoscope inserted into a coelom of a patient, there is a possibility that the cap may fall off in the coelom during an operation without being noticed by an operator that the cap has loosened.
Accordingly, the applicant, to overcome the disadvantages described above, has proposed an endoscope in Japanese Utility Model Publication Sho 61/1986-21043, in which a pin is provided on the inner peripheral surface of a cap and a fitting groove is provided on the outer peripheral surface of a distal end member of the endoscope such that the cap is rotated and drawn in the distal end member while the pin is fitted therein Such an endoscope will be described hereinafter with reference to FIGS. 1A and 1B to 4.
In FIG. 1A which is a diagram of the distal end of an endoscope with its inner structure omitted, a cap screw body 8 is rotatably fitted on the outer periphery of the distal end 1 of the endoscope so as not to fall off therefrom by limiting its axial position A male thread 11 is provided on the front outer peripheral surface of the cap screw body 8 such that a cap 14 is mounted on the distal end member 1 by threadably engaging a female thread 13 provided on the rear inner peripheral surface of the cap 14 with the male thread 11. An observation window 16 and an illumination window 17 are arranged on the distal end surface 15 of the cap 14 as shown in FIG. 1B. A pin 18 is provided on the inner peripheral surface of the cap 14 so as to project inwardly thereof (FIG. 2). The pin 18 is fitted into a peripheral groove 19b which is a strucuural element of a fitting groove 19 formed on the distal outer peripheral surface of the distal end member 1. The fitting groove 19 is formed in a crank-shaped configuration including axial grooves 19a and 19c and a peripheral groove 19b as shown in FIG. 4.
To mount the cap 14 on the distal end member 1, after the cap 14 is fitted on the distal end member 1 along the axial groove 19a thereof, the cap screw body 8 is rotated. Then, the cap 14 having the female thread 13 which engages the male thread 11 is fixed in place with rectilinear and rotational movements along the fitting groove 19 such that the observation and the illumination windows 16, 17 face the observation and illumination optical systems, respectively.
Accordingly, even if the cap 14 thus mounted loosens during observation, there is no possibility that the cap 14 falls off from the distal end member since the pin 18 stops on the front end side of the axial groove 19c. In addition, when the cap 14 loosens and the pin 18 moves to a position shown in FIG. 4, the observation and the illumination windows 16, 17 are shifted to positions shown in FIG. 3 by solid lines to reduce brightness, making an observed image dark and defective, so that an operator can discover that the cap 14 is loose.
In the disclosure of the Japanese Utility Model Publication described above, while the pin 18 moves along the fitting groove 19, the cap 14 is always in threadable engagement with the cap screw body 8. While the pin 18 moves along the axial grooves 19a and 19c, as shown in FIG. 4, only the cap screw body 8 is rotated, so that there is no problem. While the pin 18 moves along the peripheral groove 19b, however, only the cap 14 is rotated. At this time, since the cap screw body 8 is not moved and only the cap 14 is rotated, the pin 18 moves along an angle of inclination .alpha..sub.0 of the male thread 11 (a lead angle) (see FIG. 4), so that the pin 18 may be pushed against the side wall of the peripheral groove 19b by the threading action to be brought into contact therewith and to cause binding between the male thread 11 and the female thread 13. Thus, there are problems that the cap 14 may not be removed or set up.